A sensor network is a core technical infrastructure for realizing a ubiquitous computing technology, and may operate by connecting each sensor node in a wired or wireless manner. Since each node of the sensor network operates using a battery having a limited capacity, it is a top priority concern to transmit sensing data with minimum energy. In addition, in order to apply the sensor network to a real-time system, time delay in a large sensor network should be minimized. Therefore, a sensor network adopting real-time monitoring is required to use a protocol having little time delay on the network while minimizing battery consumption.
Each node included in the wireless sensor network (WSN) performs tasks such as sensing of information on surrounding conditions, computing, and wireless communication using a battery having a limited capacity. If typical media access control (MAC) protocols such as MANET or IEEE802.11 are applied to the sensor network, the wireless network will experience problems in energy consumption such as packet collision/latency, overhearing, control packet overhead, and idle listening. Particularly, in the idle listening, since the sensor node operates in an active state even when a communication function is not required, large energy consumption is generated. In order to overcome these shortcomings, the MAC protocol used in the sensor network has been designed to save power consumption by operating in a sleep state during a normal condition and periodically waking up to operate in an active state. Such a method is employed in some sensor MAC protocols such as Sensor-MAC, Timeout-MAC, and B-MAC.
However, the aforementioned sensor MAC protocols are short of energy efficiency. In addition, if a duty cycle is reduced to increase energy efficiency, network delay accordingly increases. That is, since the energy efficiency and the network delay trade off each other, the aforementioned sensor network protocols would have problems when a real-time application is required with a limited capacity of the power source such as a battery.
In order to solve these problems, Korean Registered Patent Document No. 10-656385, entitled “Real-time Sensor Line Protocol” proposed a linear structure communication protocol applied to a wireless sensor network. However, according to the communication protocol proposed in the above patent document, while it is possible to generally provide an efficient wireless sensor network, it fails to provide downstream for transmitting data or commands from a sink node to a terminal node.
For this reason, the applicant is to propose a protocol capable of efficiently performing reliable bidirectional communication between the sink node and the terminal node in a wireless sensor network having a linear structure.